src/librustc/hir/lowering/item.rs

   1 use super::LoweringContext;
   2 use super::ImplTraitContext;
   3 use super::ImplTraitPosition;
   4 use super::ImplTraitTypeIdVisitor;
   5 use super::AnonymousLifetimeMode;
   6 use super::ParamMode;
   7
   8 use crate::hir::{self, HirVec};
   9 use crate::hir::ptr::P;
  10 use crate::hir::def_id::DefId;
  11 use crate::hir::def::{Res, DefKind};
  12 use crate::util::nodemap::NodeMap;
  13
  14 use rustc_data_structures::thin_vec::ThinVec;
  15 use rustc_target::spec::abi;
  16
  17 use std::collections::BTreeSet;
  18 use smallvec::SmallVec;
  19 use syntax::attr;
  20 use syntax::ast::*;
  21 use syntax::visit::{self, Visitor};
  22 use syntax::source_map::{respan, DesugaringKind};
  23 use syntax::symbol::{kw, sym};
  24 use syntax_pos::Span;
  25
  26 use rustc_error_codes::*;
  27
  28 pub(super) struct ItemLowerer<'tcx, 'interner> {
  29     pub(super) lctx: &'tcx mut LoweringContext<'interner>,
  30 }
  31
  32 impl<'tcx, 'interner> ItemLowerer<'tcx, 'interner> {
  33     fn with_trait_impl_ref<F>(&mut self, trait_impl_ref: &Option<TraitRef>, f: F)
  34     where
  35         F: FnOnce(&mut Self),
  36     {
  37         let old = self.lctx.is_in_trait_impl;
  38         self.lctx.is_in_trait_impl = if let &None = trait_impl_ref {
  39             false
  40         } else {
  41             true
  42         };
  43         f(self);
  44         self.lctx.is_in_trait_impl = old;
  45     }
  46 }
  47
  48 impl<'tcx, 'interner> Visitor<'tcx> for ItemLowerer<'tcx, 'interner> {
  49     fn visit_mod(&mut self, m: &'tcx Mod, _s: Span, _attrs: &[Attribute], n: NodeId) {
  50         let hir_id = self.lctx.lower_node_id(n);
  51
  52         self.lctx.modules.insert(hir_id, hir::ModuleItems {
  53             items: BTreeSet::new(),
  54             trait_items: BTreeSet::new(),
  55             impl_items: BTreeSet::new(),
  56         });
  57
  58         let old = self.lctx.current_module;
  59         self.lctx.current_module = hir_id;
  60         visit::walk_mod(self, m);
  61         self.lctx.current_module = old;
  62     }
  63
  64     fn visit_item(&mut self, item: &'tcx Item) {
  65         let mut item_hir_id = None;
  66         self.lctx.with_hir_id_owner(item.id, |lctx| {
  67             lctx.without_in_scope_lifetime_defs(|lctx| {
  68                 if let Some(hir_item) = lctx.lower_item(item) {
  69                     item_hir_id = Some(hir_item.hir_id);
  70                     lctx.insert_item(hir_item);
  71                 }
  72             })
  73         });
  74
  75         if let Some(hir_id) = item_hir_id {
  76             self.lctx.with_parent_item_lifetime_defs(hir_id, |this| {
  77                 let this = &mut ItemLowerer { lctx: this };
  78                 if let ItemKind::Impl(.., ref opt_trait_ref, _, _) = item.kind {
  79                     this.with_trait_impl_ref(opt_trait_ref, |this| {
  80                         visit::walk_item(this, item)
  81                     });
  82                 } else {
  83                     visit::walk_item(this, item);
  84                 }
  85             });
  86         }
  87     }
  88
  89     fn visit_trait_item(&mut self, item: &'tcx AssocItem) {
  90         self.lctx.with_hir_id_owner(item.id, |lctx| {
  91             let hir_item = lctx.lower_trait_item(item);
  92             let id = hir::TraitItemId { hir_id: hir_item.hir_id };
  93             lctx.trait_items.insert(id, hir_item);
  94             lctx.modules.get_mut(&lctx.current_module).unwrap().trait_items.insert(id);
  95         });
  96
  97         visit::walk_trait_item(self, item);
  98     }
  99
 100     fn visit_impl_item(&mut self, item: &'tcx AssocItem) {
 101         self.lctx.with_hir_id_owner(item.id, |lctx| {
 102             let hir_item = lctx.lower_impl_item(item);
 103             let id = hir::ImplItemId { hir_id: hir_item.hir_id };
 104             lctx.impl_items.insert(id, hir_item);
 105             lctx.modules.get_mut(&lctx.current_module).unwrap().impl_items.insert(id);
 106         });
 107         visit::walk_impl_item(self, item);
 108     }
 109 }
 110
 111 impl LoweringContext<'_> {
 112     // Same as the method above, but accepts `hir::GenericParam`s
 113     // instead of `ast::GenericParam`s.
 114     // This should only be used with generics that have already had their
 115     // in-band lifetimes added. In practice, this means that this function is
 116     // only used when lowering a child item of a trait or impl.
 117     fn with_parent_item_lifetime_defs<T>(
 118         &mut self,
 119         parent_hir_id: hir::HirId,
 120         f: impl FnOnce(&mut LoweringContext<'_>) -> T,
 121     ) -> T {
 122         let old_len = self.in_scope_lifetimes.len();
 123
 124         let parent_generics = match self.items.get(&parent_hir_id).unwrap().kind {
 125             hir::ItemKind::Impl(_, _, _, ref generics, ..)
 126             | hir::ItemKind::Trait(_, _, ref generics, ..) => {
 127                 &generics.params[..]
 128             }
 129             _ => &[],
 130         };
 131         let lt_def_names = parent_generics.iter().filter_map(|param| match param.kind {
 132             hir::GenericParamKind::Lifetime { .. } => Some(param.name.modern()),
 133             _ => None,
 134         });
 135         self.in_scope_lifetimes.extend(lt_def_names);
 136
 137         let res = f(self);
 138
 139         self.in_scope_lifetimes.truncate(old_len);
 140         res
 141     }
 142
 143     // Clears (and restores) the `in_scope_lifetimes` field. Used when
 144     // visiting nested items, which never inherit in-scope lifetimes
 145     // from their surrounding environment.
 146     fn without_in_scope_lifetime_defs<T>(
 147         &mut self,
 148         f: impl FnOnce(&mut LoweringContext<'_>) -> T,
 149     ) -> T {
 150         let old_in_scope_lifetimes = std::mem::replace(&mut self.in_scope_lifetimes, vec![]);
 151
 152         // this vector is only used when walking over impl headers,
 153         // input types, and the like, and should not be non-empty in
 154         // between items
 155         assert!(self.lifetimes_to_define.is_empty());
 156
 157         let res = f(self);
 158
 159         assert!(self.in_scope_lifetimes.is_empty());
 160         self.in_scope_lifetimes = old_in_scope_lifetimes;
 161
 162         res
 163     }
 164
 165     pub(super) fn lower_mod(&mut self, m: &Mod) -> hir::Mod {
 166         hir::Mod {
 167             inner: m.inner,
 168             item_ids: m.items.iter().flat_map(|x| self.lower_item_id(x)).collect(),
 169         }
 170     }
 171
 172     pub(super) fn lower_item_id(&mut self, i: &Item) -> SmallVec<[hir::ItemId; 1]> {
 173         let node_ids = match i.kind {
 174             ItemKind::Use(ref use_tree) => {
 175                 let mut vec = smallvec![i.id];
 176                 self.lower_item_id_use_tree(use_tree, i.id, &mut vec);
 177                 vec
 178             }
 179             ItemKind::MacroDef(..) => SmallVec::new(),
 180             ItemKind::Fn(..) |
 181             ItemKind::Impl(.., None, _, _) => smallvec![i.id],
 182             ItemKind::Static(ref ty, ..) => {
 183                 let mut ids = smallvec![i.id];
 184                 if self.sess.features_untracked().impl_trait_in_bindings {
 185                     let mut visitor = ImplTraitTypeIdVisitor { ids: &mut ids };
 186                     visitor.visit_ty(ty);
 187                 }
 188                 ids
 189             },
 190             ItemKind::Const(ref ty, ..) => {
 191                 let mut ids = smallvec![i.id];
 192                 if self.sess.features_untracked().impl_trait_in_bindings {
 193                     let mut visitor = ImplTraitTypeIdVisitor { ids: &mut ids };
 194                     visitor.visit_ty(ty);
 195                 }
 196                 ids
 197             },
 198             _ => smallvec![i.id],
 199         };
 200
 201         node_ids.into_iter().map(|node_id| hir::ItemId {
 202             id: self.allocate_hir_id_counter(node_id)
 203         }).collect()
 204     }
 205
 206     fn lower_item_id_use_tree(
 207         &mut self,
 208         tree: &UseTree,
 209         base_id: NodeId,
 210         vec: &mut SmallVec<[NodeId; 1]>
 211     ) {
 212         match tree.kind {
 213             UseTreeKind::Nested(ref nested_vec) => for &(ref nested, id) in nested_vec {
 214                 vec.push(id);
 215                 self.lower_item_id_use_tree(nested, id, vec);
 216             },
 217             UseTreeKind::Glob => {}
 218             UseTreeKind::Simple(_, id1, id2) => {
 219                 for (_, &id) in self.expect_full_res_from_use(base_id)
 220                                     .skip(1)
 221                                     .zip([id1, id2].iter())
 222                 {
 223                     vec.push(id);
 224                 }
 225             },
 226         }
 227     }
 228
 229     pub fn lower_item(&mut self, i: &Item) -> Option<hir::Item> {
 230         let mut ident = i.ident;
 231         let mut vis = self.lower_visibility(&i.vis, None);
 232         let attrs = self.lower_attrs(&i.attrs);
 233
 234         if let ItemKind::MacroDef(ref def) = i.kind {
 235             if !def.legacy || attr::contains_name(&i.attrs, sym::macro_export) {
 236                 let body = self.lower_token_stream(def.body.inner_tokens());
 237                 let hir_id = self.lower_node_id(i.id);
 238                 self.exported_macros.push(hir::MacroDef {
 239                     name: ident.name,
 240                     vis,
 241                     attrs,
 242                     hir_id,
 243                     span: i.span,
 244                     body,
 245                     legacy: def.legacy,
 246                 });
 247             } else {
 248                 self.non_exported_macro_attrs.extend(attrs.into_iter());
 249             }
 250             return None;
 251         }
 252
 253         let kind = self.lower_item_kind(i.span, i.id, &mut ident, &attrs, &mut vis, &i.kind);
 254
 255         Some(hir::Item {
 256             hir_id: self.lower_node_id(i.id),
 257             ident,
 258             attrs,
 259             kind,
 260             vis,
 261             span: i.span,
 262         })
 263     }
 264
 265     fn lower_item_kind(
 266         &mut self,
 267         span: Span,
 268         id: NodeId,
 269         ident: &mut Ident,
 270         attrs: &hir::HirVec<Attribute>,
 271         vis: &mut hir::Visibility,
 272         i: &ItemKind,
 273     ) -> hir::ItemKind {
 274         match *i {
 275             ItemKind::ExternCrate(orig_name) => hir::ItemKind::ExternCrate(orig_name),
 276             ItemKind::Use(ref use_tree) => {
 277                 // Start with an empty prefix.
 278                 let prefix = Path {
 279                     segments: vec![],
 280                     span: use_tree.span,
 281                 };
 282
 283                 self.lower_use_tree(use_tree, &prefix, id, vis, ident, attrs)
 284             }
 285             ItemKind::Static(ref t, m, ref e) => {
 286                 hir::ItemKind::Static(
 287                     self.lower_ty(
 288                         t,
 289                         if self.sess.features_untracked().impl_trait_in_bindings {
 290                             ImplTraitContext::OpaqueTy(None)
 291                         } else {
 292                             ImplTraitContext::Disallowed(ImplTraitPosition::Binding)
 293                         }
 294                     ),
 295                     m,
 296                     self.lower_const_body(span, Some(e)),
 297                 )
 298             }
 299             ItemKind::Const(ref t, ref e) => {
 300                 hir::ItemKind::Const(
 301                     self.lower_ty(
 302                         t,
 303                         if self.sess.features_untracked().impl_trait_in_bindings {
 304                             ImplTraitContext::OpaqueTy(None)
 305                         } else {
 306                             ImplTraitContext::Disallowed(ImplTraitPosition::Binding)
 307                         }
 308                     ),
 309                     self.lower_const_body(span, Some(e))
 310                 )
 311             }
 312             ItemKind::Fn(FnSig { ref decl, header }, ref generics, ref body) => {
 313                 let fn_def_id = self.resolver.definitions().local_def_id(id);
 314                 self.with_new_scopes(|this| {
 315                     this.current_item = Some(ident.span);
 316
 317                     // Note: we don't need to change the return type from `T` to
 318                     // `impl Future<Output = T>` here because lower_body
 319                     // only cares about the input argument patterns in the function
 320                     // declaration (decl), not the return types.
 321                     let body_id = this.lower_maybe_async_body(
 322                         span,
 323                         &decl,
 324                         header.asyncness.node,
 325                         Some(body),
 326                     );
 327
 328                     let (generics, decl) = this.add_in_band_defs(
 329                         generics,
 330                         fn_def_id,
 331                         AnonymousLifetimeMode::PassThrough,
 332                         |this, idty| this.lower_fn_decl(
 333                             &decl,
 334                             Some((fn_def_id, idty)),
 335                             true,
 336                             header.asyncness.node.opt_return_id()
 337                         ),
 338                     );
 339                     let sig = hir::FnSig { decl, header: this.lower_fn_header(header) };
 340                     hir::ItemKind::Fn(sig, generics, body_id)
 341                 })
 342             }
 343             ItemKind::Mod(ref m) => hir::ItemKind::Mod(self.lower_mod(m)),
 344             ItemKind::ForeignMod(ref nm) => hir::ItemKind::ForeignMod(self.lower_foreign_mod(nm)),
 345             ItemKind::GlobalAsm(ref ga) => hir::ItemKind::GlobalAsm(self.lower_global_asm(ga)),
 346             ItemKind::TyAlias(ref ty, ref generics) => match ty.kind.opaque_top_hack() {
 347                 None => {
 348                     let ty = self.lower_ty(ty, ImplTraitContext::disallowed());
 349                     let generics = self.lower_generics(generics, ImplTraitContext::disallowed());
 350                     hir::ItemKind::TyAlias(ty, generics)
 351                 },
 352                 Some(bounds) => {
 353                     let ty = hir::OpaqueTy {
 354                         generics: self.lower_generics(generics, ImplTraitContext::OpaqueTy(None)),
 355                         bounds: self.lower_param_bounds(bounds, ImplTraitContext::OpaqueTy(None)),
 356                         impl_trait_fn: None,
 357                         origin: hir::OpaqueTyOrigin::TypeAlias,
 358                     };
 359                     hir::ItemKind::OpaqueTy(ty)
 360                 }
 361             }
 362             ItemKind::Enum(ref enum_definition, ref generics) => {
 363                 hir::ItemKind::Enum(
 364                     hir::EnumDef {
 365                         variants: enum_definition
 366                             .variants
 367                             .iter()
 368                             .map(|x| self.lower_variant(x))
 369                             .collect(),
 370                     },
 371                     self.lower_generics(generics, ImplTraitContext::disallowed()),
 372                 )
 373             },
 374             ItemKind::Struct(ref struct_def, ref generics) => {
 375                 let struct_def = self.lower_variant_data(struct_def);
 376                 hir::ItemKind::Struct(
 377                     struct_def,
 378                     self.lower_generics(generics, ImplTraitContext::disallowed()),
 379                 )
 380             }
 381             ItemKind::Union(ref vdata, ref generics) => {
 382                 let vdata = self.lower_variant_data(vdata);
 383                 hir::ItemKind::Union(
 384                     vdata,
 385                     self.lower_generics(generics, ImplTraitContext::disallowed()),
 386                 )
 387             }
 388             ItemKind::Impl(
 389                 unsafety,
 390                 polarity,
 391                 defaultness,
 392                 ref ast_generics,
 393                 ref trait_ref,
 394                 ref ty,
 395                 ref impl_items,
 396             ) => {
 397                 let def_id = self.resolver.definitions().local_def_id(id);
 398
 399                 // Lower the "impl header" first. This ordering is important
 400                 // for in-band lifetimes! Consider `'a` here:
 401                 //
 402                 //     impl Foo<'a> for u32 {
 403                 //         fn method(&'a self) { .. }
 404                 //     }
 405                 //
 406                 // Because we start by lowering the `Foo<'a> for u32`
 407                 // part, we will add `'a` to the list of generics on
 408                 // the impl. When we then encounter it later in the
 409                 // method, it will not be considered an in-band
 410                 // lifetime to be added, but rather a reference to a
 411                 // parent lifetime.
 412                 let lowered_trait_impl_id = self.lower_node_id(id);
 413                 let (generics, (trait_ref, lowered_ty)) = self.add_in_band_defs(
 414                     ast_generics,
 415                     def_id,
 416                     AnonymousLifetimeMode::CreateParameter,
 417                     |this, _| {
 418                         let trait_ref = trait_ref.as_ref().map(|trait_ref| {
 419                             this.lower_trait_ref(trait_ref, ImplTraitContext::disallowed())
 420                         });
 421
 422                         if let Some(ref trait_ref) = trait_ref {
 423                             if let Res::Def(DefKind::Trait, def_id) = trait_ref.path.res {
 424                                 this.trait_impls.entry(def_id).or_default().push(
 425                                     lowered_trait_impl_id);
 426                             }
 427                         }
 428
 429                         let lowered_ty = this.lower_ty(ty, ImplTraitContext::disallowed());
 430
 431                         (trait_ref, lowered_ty)
 432                     },
 433                 );
 434
 435                 let new_impl_items = self.with_in_scope_lifetime_defs(
 436                     &ast_generics.params,
 437                     |this| {
 438                         impl_items
 439                             .iter()
 440                             .map(|item| this.lower_impl_item_ref(item))
 441                             .collect()
 442                     },
 443                 );
 444
 445                 hir::ItemKind::Impl(
 446                     unsafety,
 447                     polarity,
 448                     self.lower_defaultness(defaultness, true /* [1] */),
 449                     generics,
 450                     trait_ref,
 451                     lowered_ty,
 452                     new_impl_items,
 453                 )
 454             }
 455             ItemKind::Trait(is_auto, unsafety, ref generics, ref bounds, ref items) => {
 456                 let bounds = self.lower_param_bounds(bounds, ImplTraitContext::disallowed());
 457                 let items = items
 458                     .iter()
 459                     .map(|item| self.lower_trait_item_ref(item))
 460                     .collect();
 461                 hir::ItemKind::Trait(
 462                     is_auto,
 463                     unsafety,
 464                     self.lower_generics(generics, ImplTraitContext::disallowed()),
 465                     bounds,
 466                     items,
 467                 )
 468             }
 469             ItemKind::TraitAlias(ref generics, ref bounds) => hir::ItemKind::TraitAlias(
 470                 self.lower_generics(generics, ImplTraitContext::disallowed()),
 471                 self.lower_param_bounds(bounds, ImplTraitContext::disallowed()),
 472             ),
 473             ItemKind::MacroDef(..)
 474             | ItemKind::Mac(..) => bug!("`TyMac` should have been expanded by now"),
 475         }
 476
 477         // [1] `defaultness.has_value()` is never called for an `impl`, always `true` in order to
 478         //     not cause an assertion failure inside the `lower_defaultness` function.
 479     }
 480
 481     fn lower_use_tree(
 482         &mut self,
 483         tree: &UseTree,
 484         prefix: &Path,
 485         id: NodeId,
 486         vis: &mut hir::Visibility,
 487         ident: &mut Ident,
 488         attrs: &hir::HirVec<Attribute>,
 489     ) -> hir::ItemKind {
 490         debug!("lower_use_tree(tree={:?})", tree);
 491         debug!("lower_use_tree: vis = {:?}", vis);
 492
 493         let path = &tree.prefix;
 494         let segments = prefix
 495             .segments
 496             .iter()
 497             .chain(path.segments.iter())
 498             .cloned()
 499             .collect();
 500
 501         match tree.kind {
 502             UseTreeKind::Simple(rename, id1, id2) => {
 503                 *ident = tree.ident();
 504
 505                 // First, apply the prefix to the path.
 506                 let mut path = Path {
 507                     segments,
 508                     span: path.span,
 509                 };
 510
 511                 // Correctly resolve `self` imports.
 512                 if path.segments.len() > 1
 513                     && path.segments.last().unwrap().ident.name == kw::SelfLower
 514                 {
 515                     let _ = path.segments.pop();
 516                     if rename.is_none() {
 517                         *ident = path.segments.last().unwrap().ident;
 518                     }
 519                 }
 520
 521                 let mut resolutions = self.expect_full_res_from_use(id);
 522                 // We want to return *something* from this function, so hold onto the first item
 523                 // for later.
 524                 let ret_res = self.lower_res(resolutions.next().unwrap_or(Res::Err));
 525
 526                 // Here, we are looping over namespaces, if they exist for the definition
 527                 // being imported. We only handle type and value namespaces because we
 528                 // won't be dealing with macros in the rest of the compiler.
 529                 // Essentially a single `use` which imports two names is desugared into
 530                 // two imports.
 531                 for (res, &new_node_id) in resolutions.zip([id1, id2].iter()) {
 532                     let ident = *ident;
 533                     let mut path = path.clone();
 534                     for seg in &mut path.segments {
 535                         seg.id = self.resolver.next_node_id();
 536                     }
 537                     let span = path.span;
 538
 539                     self.with_hir_id_owner(new_node_id, |this| {
 540                         let new_id = this.lower_node_id(new_node_id);
 541                         let res = this.lower_res(res);
 542                         let path =
 543                             this.lower_path_extra(res, &path, ParamMode::Explicit, None);
 544                         let kind = hir::ItemKind::Use(P(path), hir::UseKind::Single);
 545                         let vis = this.rebuild_vis(&vis);
 546
 547                         this.insert_item(
 548                             hir::Item {
 549                                 hir_id: new_id,
 550                                 ident,
 551                                 attrs: attrs.into_iter().cloned().collect(),
 552                                 kind,
 553                                 vis,
 554                                 span,
 555                             },
 556                         );
 557                     });
 558                 }
 559
 560                 let path = P(self.lower_path_extra(ret_res, &path, ParamMode::Explicit, None));
 561                 hir::ItemKind::Use(path, hir::UseKind::Single)
 562             }
 563             UseTreeKind::Glob => {
 564                 let path = P(self.lower_path(
 565                     id,
 566                     &Path {
 567                         segments,
 568                         span: path.span,
 569                     },
 570                     ParamMode::Explicit,
 571                 ));
 572                 hir::ItemKind::Use(path, hir::UseKind::Glob)
 573             }
 574             UseTreeKind::Nested(ref trees) => {
 575                 // Nested imports are desugared into simple imports.
 576                 // So, if we start with
 577                 //
 578                 // ```
 579                 // pub(x) use foo::{a, b};
 580                 // ```
 581                 //
 582                 // we will create three items:
 583                 //
 584                 // ```
 585                 // pub(x) use foo::a;
 586                 // pub(x) use foo::b;
 587                 // pub(x) use foo::{}; // <-- this is called the `ListStem`
 588                 // ```
 589                 //
 590                 // The first two are produced by recursively invoking
 591                 // `lower_use_tree` (and indeed there may be things
 592                 // like `use foo::{a::{b, c}}` and so forth).  They
 593                 // wind up being directly added to
 594                 // `self.items`. However, the structure of this
 595                 // function also requires us to return one item, and
 596                 // for that we return the `{}` import (called the
 597                 // `ListStem`).
 598
 599                 let prefix = Path {
 600                     segments,
 601                     span: prefix.span.to(path.span),
 602                 };
 603
 604                 // Add all the nested `PathListItem`s to the HIR.
 605                 for &(ref use_tree, id) in trees {
 606                     let new_hir_id = self.lower_node_id(id);
 607
 608                     let mut prefix = prefix.clone();
 609
 610                     // Give the segments new node-ids since they are being cloned.
 611                     for seg in &mut prefix.segments {
 612                         seg.id = self.resolver.next_node_id();
 613                     }
 614
 615                     // Each `use` import is an item and thus are owners of the
 616                     // names in the path. Up to this point the nested import is
 617                     // the current owner, since we want each desugared import to
 618                     // own its own names, we have to adjust the owner before
 619                     // lowering the rest of the import.
 620                     self.with_hir_id_owner(id, |this| {
 621                         let mut vis = this.rebuild_vis(&vis);
 622                         let mut ident = *ident;
 623
 624                         let kind = this.lower_use_tree(use_tree,
 625                                                        &prefix,
 626                                                        id,
 627                                                        &mut vis,
 628                                                        &mut ident,
 629                                                        attrs);
 630
 631                         this.insert_item(
 632                             hir::Item {
 633                                 hir_id: new_hir_id,
 634                                 ident,
 635                                 attrs: attrs.into_iter().cloned().collect(),
 636                                 kind,
 637                                 vis,
 638                                 span: use_tree.span,
 639                             },
 640                         );
 641                     });
 642                 }
 643
 644                 // Subtle and a bit hacky: we lower the privacy level
 645                 // of the list stem to "private" most of the time, but
 646                 // not for "restricted" paths. The key thing is that
 647                 // we don't want it to stay as `pub` (with no caveats)
 648                 // because that affects rustdoc and also the lints
 649                 // about `pub` items. But we can't *always* make it
 650                 // private -- particularly not for restricted paths --
 651                 // because it contains node-ids that would then be
 652                 // unused, failing the check that HirIds are "densely
 653                 // assigned".
 654                 match vis.node {
 655                     hir::VisibilityKind::Public |
 656                     hir::VisibilityKind::Crate(_) |
 657                     hir::VisibilityKind::Inherited => {
 658                         *vis = respan(prefix.span.shrink_to_lo(), hir::VisibilityKind::Inherited);
 659                     }
 660                     hir::VisibilityKind::Restricted { .. } => {
 661                         // Do nothing here, as described in the comment on the match.
 662                     }
 663                 }
 664
 665                 let res = self.expect_full_res_from_use(id).next().unwrap_or(Res::Err);
 666                 let res = self.lower_res(res);
 667                 let path = P(self.lower_path_extra(res, &prefix, ParamMode::Explicit, None));
 668                 hir::ItemKind::Use(path, hir::UseKind::ListStem)
 669             }
 670         }
 671     }
 672
 673     /// Paths like the visibility path in `pub(super) use foo::{bar, baz}` are repeated
 674     /// many times in the HIR tree; for each occurrence, we need to assign distinct
 675     /// `NodeId`s. (See, e.g., #56128.)
 676     fn rebuild_use_path(&mut self, path: &hir::Path) -> hir::Path {
 677         debug!("rebuild_use_path(path = {:?})", path);
 678         let segments = path.segments.iter().map(|seg| hir::PathSegment {
 679             ident: seg.ident,
 680             hir_id: seg.hir_id.map(|_| self.next_id()),
 681             res: seg.res,
 682             args: None,
 683             infer_args: seg.infer_args,
 684         }).collect();
 685         hir::Path {
 686             span: path.span,
 687             res: path.res,
 688             segments,
 689         }
 690     }
 691
 692     fn rebuild_vis(&mut self, vis: &hir::Visibility) -> hir::Visibility {
 693         let vis_kind = match vis.node {
 694             hir::VisibilityKind::Public => hir::VisibilityKind::Public,
 695             hir::VisibilityKind::Crate(sugar) => hir::VisibilityKind::Crate(sugar),
 696             hir::VisibilityKind::Inherited => hir::VisibilityKind::Inherited,
 697             hir::VisibilityKind::Restricted { ref path, hir_id: _ } => {
 698                 hir::VisibilityKind::Restricted {
 699                     path: P(self.rebuild_use_path(path)),
 700                     hir_id: self.next_id(),
 701                 }
 702             }
 703         };
 704         respan(vis.span, vis_kind)
 705     }
 706
 707     fn lower_foreign_item(&mut self, i: &ForeignItem) -> hir::ForeignItem {
 708         let def_id = self.resolver.definitions().local_def_id(i.id);
 709         hir::ForeignItem {
 710             hir_id: self.lower_node_id(i.id),
 711             ident: i.ident,
 712             attrs: self.lower_attrs(&i.attrs),
 713             kind: match i.kind {
 714                 ForeignItemKind::Fn(ref fdec, ref generics) => {
 715                     let (generics, (fn_dec, fn_args)) = self.add_in_band_defs(
 716                         generics,
 717                         def_id,
 718                         AnonymousLifetimeMode::PassThrough,
 719                         |this, _| {
 720                             (
 721                                 // Disallow `impl Trait` in foreign items.
 722                                 this.lower_fn_decl(fdec, None, false, None),
 723                                 this.lower_fn_params_to_names(fdec),
 724                             )
 725                         },
 726                     );
 727
 728                     hir::ForeignItemKind::Fn(fn_dec, fn_args, generics)
 729                 }
 730                 ForeignItemKind::Static(ref t, m) => {
 731                     hir::ForeignItemKind::Static(
 732                         self.lower_ty(t, ImplTraitContext::disallowed()), m)
 733                 }
 734                 ForeignItemKind::Ty => hir::ForeignItemKind::Type,
 735                 ForeignItemKind::Macro(_) => panic!("macro shouldn't exist here"),
 736             },
 737             vis: self.lower_visibility(&i.vis, None),
 738             span: i.span,
 739         }
 740     }
 741
 742     fn lower_foreign_mod(&mut self, fm: &ForeignMod) -> hir::ForeignMod {
 743         hir::ForeignMod {
 744             abi: fm.abi.map_or(abi::Abi::C, |abi| self.lower_abi(abi)),
 745             items: fm.items
 746                 .iter()
 747                 .map(|x| self.lower_foreign_item(x))
 748                 .collect(),
 749         }
 750     }
 751
 752     fn lower_global_asm(&mut self, ga: &GlobalAsm) -> P<hir::GlobalAsm> {
 753         P(hir::GlobalAsm { asm: ga.asm })
 754     }
 755
 756     fn lower_variant(&mut self, v: &Variant) -> hir::Variant {
 757         hir::Variant {
 758             attrs: self.lower_attrs(&v.attrs),
 759             data: self.lower_variant_data(&v.data),
 760             disr_expr: v.disr_expr.as_ref().map(|e| self.lower_anon_const(e)),
 761             id: self.lower_node_id(v.id),
 762             ident: v.ident,
 763             span: v.span,
 764         }
 765     }
 766
 767     fn lower_variant_data(&mut self, vdata: &VariantData) -> hir::VariantData {
 768         match *vdata {
 769             VariantData::Struct(ref fields, recovered) => hir::VariantData::Struct(
 770                 fields.iter().enumerate().map(|f| self.lower_struct_field(f)).collect(),
 771                 recovered,
 772             ),
 773             VariantData::Tuple(ref fields, id) => {
 774                 hir::VariantData::Tuple(
 775                     fields
 776                         .iter()
 777                         .enumerate()
 778                         .map(|f| self.lower_struct_field(f))
 779                         .collect(),
 780                     self.lower_node_id(id),
 781                 )
 782             },
 783             VariantData::Unit(id) => {
 784                 hir::VariantData::Unit(self.lower_node_id(id))
 785             },
 786         }
 787     }
 788
 789     fn lower_struct_field(&mut self, (index, f): (usize, &StructField)) -> hir::StructField {
 790         let ty = if let TyKind::Path(ref qself, ref path) = f.ty.kind {
 791             let t = self.lower_path_ty(
 792                 &f.ty,
 793                 qself,
 794                 path,
 795                 ParamMode::ExplicitNamed, // no `'_` in declarations (Issue #61124)
 796                 ImplTraitContext::disallowed()
 797             );
 798             P(t)
 799         } else {
 800             self.lower_ty(&f.ty, ImplTraitContext::disallowed())
 801         };
 802         hir::StructField {
 803             span: f.span,
 804             hir_id: self.lower_node_id(f.id),
 805             ident: match f.ident {
 806                 Some(ident) => ident,
 807                 // FIXME(jseyfried): positional field hygiene.
 808                 None => Ident::new(sym::integer(index), f.span),
 809             },
 810             vis: self.lower_visibility(&f.vis, None),
 811             ty,
 812             attrs: self.lower_attrs(&f.attrs),
 813         }
 814     }
 815
 816     fn lower_trait_item(&mut self, i: &AssocItem) -> hir::TraitItem {
 817         let trait_item_def_id = self.resolver.definitions().local_def_id(i.id);
 818
 819         let (generics, kind) = match i.kind {
 820             AssocItemKind::Const(ref ty, ref default) => (
 821                 self.lower_generics(&i.generics, ImplTraitContext::disallowed()),
 822                 hir::TraitItemKind::Const(
 823                     self.lower_ty(ty, ImplTraitContext::disallowed()),
 824                     default
 825                         .as_ref()
 826                         .map(|x| self.lower_const_body(i.span, Some(x))),
 827                 ),
 828             ),
 829             AssocItemKind::Fn(ref sig, None) => {
 830                 let names = self.lower_fn_params_to_names(&sig.decl);
 831                 let (generics, sig) = self.lower_method_sig(
 832                     &i.generics,
 833                     sig,
 834                     trait_item_def_id,
 835                     false,
 836                     None,
 837                 );
 838                 (generics, hir::TraitItemKind::Method(sig, hir::TraitMethod::Required(names)))
 839             }
 840             AssocItemKind::Fn(ref sig, Some(ref body)) => {
 841                 let body_id = self.lower_fn_body_block(i.span, &sig.decl, Some(body));
 842                 let (generics, sig) = self.lower_method_sig(
 843                     &i.generics,
 844                     sig,
 845                     trait_item_def_id,
 846                     false,
 847                     None,
 848                 );
 849                 (generics, hir::TraitItemKind::Method(sig, hir::TraitMethod::Provided(body_id)))
 850             }
 851             AssocItemKind::TyAlias(ref bounds, ref default) => {
 852                 let generics = self.lower_generics(&i.generics, ImplTraitContext::disallowed());
 853                 let kind = hir::TraitItemKind::Type(
 854                     self.lower_param_bounds(bounds, ImplTraitContext::disallowed()),
 855                     default
 856                         .as_ref()
 857                         .map(|x| self.lower_ty(x, ImplTraitContext::disallowed())),
 858                 );
 859
 860                 (generics, kind)
 861             },
 862             AssocItemKind::Macro(..) => bug!("macro item shouldn't exist at this point"),
 863         };
 864
 865         hir::TraitItem {
 866             hir_id: self.lower_node_id(i.id),
 867             ident: i.ident,
 868             attrs: self.lower_attrs(&i.attrs),
 869             generics,
 870             kind,
 871             span: i.span,
 872         }
 873     }
 874
 875     fn lower_trait_item_ref(&mut self, i: &AssocItem) -> hir::TraitItemRef {
 876         let (kind, has_default) = match i.kind {
 877             AssocItemKind::Const(_, ref default) => {
 878                 (hir::AssocItemKind::Const, default.is_some())
 879             }
 880             AssocItemKind::TyAlias(_, ref default) => {
 881                 (hir::AssocItemKind::Type, default.is_some())
 882             }
 883             AssocItemKind::Fn(ref sig, ref default) => (
 884                 hir::AssocItemKind::Method {
 885                     has_self: sig.decl.has_self(),
 886                 },
 887                 default.is_some(),
 888             ),
 889             AssocItemKind::Macro(..) => unimplemented!(),
 890         };
 891         hir::TraitItemRef {
 892             id: hir::TraitItemId { hir_id: self.lower_node_id(i.id) },
 893             ident: i.ident,
 894             span: i.span,
 895             defaultness: self.lower_defaultness(Defaultness::Default, has_default),
 896             kind,
 897         }
 898     }
 899
 900     /// Construct `ExprKind::Err` for the given `span`.
 901     fn expr_err(&mut self, span: Span) -> hir::Expr {
 902         self.expr(span, hir::ExprKind::Err, ThinVec::new())
 903     }
 904
 905     fn lower_impl_item(&mut self, i: &AssocItem) -> hir::ImplItem {
 906         let impl_item_def_id = self.resolver.definitions().local_def_id(i.id);
 907
 908         let (generics, kind) = match i.kind {
 909             AssocItemKind::Const(ref ty, ref expr) => (
 910                 self.lower_generics(&i.generics, ImplTraitContext::disallowed()),
 911                 hir::ImplItemKind::Const(
 912                     self.lower_ty(ty, ImplTraitContext::disallowed()),
 913                     self.lower_const_body(i.span, expr.as_deref()),
 914                 ),
 915             ),
 916             AssocItemKind::Fn(ref sig, ref body) => {
 917                 self.current_item = Some(i.span);
 918                 let body_id = self.lower_maybe_async_body(
 919                     i.span,
 920                     &sig.decl,
 921                     sig.header.asyncness.node,
 922                     body.as_deref(),
 923                 );
 924                 let impl_trait_return_allow = !self.is_in_trait_impl;
 925                 let (generics, sig) = self.lower_method_sig(
 926                     &i.generics,
 927                     sig,
 928                     impl_item_def_id,
 929                     impl_trait_return_allow,
 930                     sig.header.asyncness.node.opt_return_id(),
 931                 );
 932
 933                 (generics, hir::ImplItemKind::Method(sig, body_id))
 934             }
 935             AssocItemKind::TyAlias(_, ref ty) => {
 936                 let generics = self.lower_generics(&i.generics, ImplTraitContext::disallowed());
 937                 let kind = match ty {
 938                     None => {
 939                         hir::ImplItemKind::TyAlias(P(self.ty(i.span, hir::TyKind::Err)))
 940                     }
 941                     Some(ty) => match ty.kind.opaque_top_hack() {
 942                         None => {
 943                             let ty = self.lower_ty(ty, ImplTraitContext::disallowed());
 944                             hir::ImplItemKind::TyAlias(ty)
 945                         }
 946                         Some(bs) => {
 947                             let bs = self.lower_param_bounds(bs, ImplTraitContext::disallowed());
 948                             hir::ImplItemKind::OpaqueTy(bs)
 949                         }
 950                     }
 951                 };
 952                 (generics, kind)
 953             },
 954             AssocItemKind::Macro(..) => bug!("`TyMac` should have been expanded by now"),
 955         };
 956
 957         hir::ImplItem {
 958             hir_id: self.lower_node_id(i.id),
 959             ident: i.ident,
 960             attrs: self.lower_attrs(&i.attrs),
 961             generics,
 962             vis: self.lower_visibility(&i.vis, None),
 963             defaultness: self.lower_defaultness(i.defaultness, true /* [1] */),
 964             kind,
 965             span: i.span,
 966         }
 967
 968         // [1] since `default impl` is not yet implemented, this is always true in impls
 969     }
 970
 971     fn lower_impl_item_ref(&mut self, i: &AssocItem) -> hir::ImplItemRef {
 972         hir::ImplItemRef {
 973             id: hir::ImplItemId { hir_id: self.lower_node_id(i.id) },
 974             ident: i.ident,
 975             span: i.span,
 976             vis: self.lower_visibility(&i.vis, Some(i.id)),
 977             defaultness: self.lower_defaultness(i.defaultness, true /* [1] */),
 978             kind: match &i.kind {
 979                 AssocItemKind::Const(..) => hir::AssocItemKind::Const,
 980                 AssocItemKind::TyAlias(_, ty) => match ty
 981                     .as_deref()
 982                     .and_then(|ty| ty.kind.opaque_top_hack())
 983                 {
 984                     None => hir::AssocItemKind::Type,
 985                     Some(_) => hir::AssocItemKind::OpaqueTy,
 986                 },
 987                 AssocItemKind::Fn(sig, _) => hir::AssocItemKind::Method {
 988                     has_self: sig.decl.has_self(),
 989                 },
 990                 AssocItemKind::Macro(..) => unimplemented!(),
 991             },
 992         }
 993
 994         // [1] since `default impl` is not yet implemented, this is always true in impls
 995     }
 996
 997     /// If an `explicit_owner` is given, this method allocates the `HirId` in
 998     /// the address space of that item instead of the item currently being
 999     /// lowered. This can happen during `lower_impl_item_ref()` where we need to
1000     /// lower a `Visibility` value although we haven't lowered the owning
1001     /// `ImplItem` in question yet.
1002     fn lower_visibility(
1003         &mut self,
1004         v: &Visibility,
1005         explicit_owner: Option<NodeId>,
1006     ) -> hir::Visibility {
1007         let node = match v.node {
1008             VisibilityKind::Public => hir::VisibilityKind::Public,
1009             VisibilityKind::Crate(sugar) => hir::VisibilityKind::Crate(sugar),
1010             VisibilityKind::Restricted { ref path, id } => {
1011                 debug!("lower_visibility: restricted path id = {:?}", id);
1012                 let lowered_id = if let Some(owner) = explicit_owner {
1013                     self.lower_node_id_with_owner(id, owner)
1014                 } else {
1015                     self.lower_node_id(id)
1016                 };
1017                 let res = self.expect_full_res(id);
1018                 let res = self.lower_res(res);
1019                 hir::VisibilityKind::Restricted {
1020                     path: P(self.lower_path_extra(
1021                         res,
1022                         path,
1023                         ParamMode::Explicit,
1024                         explicit_owner,
1025                     )),
1026                     hir_id: lowered_id,
1027                 }
1028             },
1029             VisibilityKind::Inherited => hir::VisibilityKind::Inherited,
1030         };
1031         respan(v.span, node)
1032     }
1033
1034     fn lower_defaultness(&self, d: Defaultness, has_value: bool) -> hir::Defaultness {
1035         match d {
1036             Defaultness::Default => hir::Defaultness::Default {
1037                 has_value: has_value,
1038             },
1039             Defaultness::Final => {
1040                 assert!(has_value);
1041                 hir::Defaultness::Final
1042             }
1043         }
1044     }
1045
1046     fn record_body(&mut self, params: HirVec<hir::Param>, value: hir::Expr) -> hir::BodyId {
1047         let body = hir::Body {
1048             generator_kind: self.generator_kind,
1049             params,
1050             value,
1051         };
1052         let id = body.id();
1053         self.bodies.insert(id, body);
1054         id
1055     }
1056
1057     fn lower_body(
1058         &mut self,
1059         f: impl FnOnce(&mut LoweringContext<'_>) -> (HirVec<hir::Param>, hir::Expr),
1060     ) -> hir::BodyId {
1061         let prev_gen_kind = self.generator_kind.take();
1062         let (parameters, result) = f(self);
1063         let body_id = self.record_body(parameters, result);
1064         self.generator_kind = prev_gen_kind;
1065         body_id
1066     }
1067
1068     fn lower_param(&mut self, param: &Param) -> hir::Param {
1069         hir::Param {
1070             attrs: self.lower_attrs(&param.attrs),
1071             hir_id: self.lower_node_id(param.id),
1072             pat: self.lower_pat(&param.pat),
1073             span: param.span,
1074         }
1075     }
1076
1077     pub(super) fn lower_fn_body(
1078         &mut self,
1079         decl: &FnDecl,
1080         body: impl FnOnce(&mut LoweringContext<'_>) -> hir::Expr,
1081     ) -> hir::BodyId {
1082         self.lower_body(|this| (
1083             decl.inputs.iter().map(|x| this.lower_param(x)).collect(),
1084             body(this),
1085         ))
1086     }
1087
1088     fn lower_fn_body_block(
1089         &mut self,
1090         span: Span,
1091         decl: &FnDecl,
1092         body: Option<&Block>,
1093     ) -> hir::BodyId {
1094         self.lower_fn_body(decl, |this| this.lower_block_expr_opt(span, body))
1095     }
1096
1097     fn lower_block_expr_opt(&mut self, span: Span, block: Option<&Block>) -> hir::Expr {
1098         match block {
1099             Some(block) => self.lower_block_expr(block),
1100             None => self.expr_err(span),
1101         }
1102     }
1103
1104     pub(super) fn lower_const_body(&mut self, span: Span, expr: Option<&Expr>) -> hir::BodyId {
1105         self.lower_body(|this| (hir_vec![], match expr {
1106             Some(expr) => this.lower_expr(expr),
1107             None => this.expr_err(span),
1108         }))
1109     }
1110
1111     fn lower_maybe_async_body(
1112         &mut self,
1113         span: Span,
1114         decl: &FnDecl,
1115         asyncness: IsAsync,
1116         body: Option<&Block>,
1117     ) -> hir::BodyId {
1118         let closure_id = match asyncness {
1119             IsAsync::Async { closure_id, .. } => closure_id,
1120             IsAsync::NotAsync => return self.lower_fn_body_block(span, decl, body),
1121         };
1122
1123         self.lower_body(|this| {
1124             let mut parameters: Vec<hir::Param> = Vec::new();
1125             let mut statements: Vec<hir::Stmt> = Vec::new();
1126
1127             // Async function parameters are lowered into the closure body so that they are
1128             // captured and so that the drop order matches the equivalent non-async functions.
1129             //
1130             // from:
1131             //
1132             //     async fn foo(<pattern>: <ty>, <pattern>: <ty>, <pattern>: <ty>) {
1133             //         <body>
1134             //     }
1135             //
1136             // into:
1137             //
1138             //     fn foo(__arg0: <ty>, __arg1: <ty>, __arg2: <ty>) {
1139             //       async move {
1140             //         let __arg2 = __arg2;
1141             //         let <pattern> = __arg2;
1142             //         let __arg1 = __arg1;
1143             //         let <pattern> = __arg1;
1144             //         let __arg0 = __arg0;
1145             //         let <pattern> = __arg0;
1146             //         drop-temps { <body> } // see comments later in fn for details
1147             //       }
1148             //     }
1149             //
1150             // If `<pattern>` is a simple ident, then it is lowered to a single
1151             // `let <pattern> = <pattern>;` statement as an optimization.
1152             //
1153             // Note that the body is embedded in `drop-temps`; an
1154             // equivalent desugaring would be `return { <body>
1155             // };`. The key point is that we wish to drop all the
1156             // let-bound variables and temporaries created in the body
1157             // (and its tail expression!) before we drop the
1158             // parameters (c.f. rust-lang/rust#64512).
1159             for (index, parameter) in decl.inputs.iter().enumerate() {
1160                 let parameter = this.lower_param(parameter);
1161                 let span = parameter.pat.span;
1162
1163                 // Check if this is a binding pattern, if so, we can optimize and avoid adding a
1164                 // `let <pat> = __argN;` statement. In this case, we do not rename the parameter.
1165                 let (ident, is_simple_parameter) = match parameter.pat.kind {
1166                     hir::PatKind::Binding(hir::BindingAnnotation::Unannotated, _, ident, _) =>
1167                         (ident, true),
1168                     _ => {
1169                         // Replace the ident for bindings that aren't simple.
1170                         let name = format!("__arg{}", index);
1171                         let ident = Ident::from_str(&name);
1172
1173                         (ident, false)
1174                     },
1175                 };
1176
1177                 let desugared_span =
1178                     this.mark_span_with_reason(DesugaringKind::Async, span, None);
1179
1180                 // Construct a parameter representing `__argN: <ty>` to replace the parameter of the
1181                 // async function.
1182                 //
1183                 // If this is the simple case, this parameter will end up being the same as the
1184                 // original parameter, but with a different pattern id.
1185                 let mut stmt_attrs = ThinVec::new();
1186                 stmt_attrs.extend(parameter.attrs.iter().cloned());
1187                 let (new_parameter_pat, new_parameter_id) = this.pat_ident(desugared_span, ident);
1188                 let new_parameter = hir::Param {
1189                     attrs: parameter.attrs,
1190                     hir_id: parameter.hir_id,
1191                     pat: new_parameter_pat,
1192                     span: parameter.span,
1193                 };
1194
1195
1196                 if is_simple_parameter {
1197                     // If this is the simple case, then we only insert one statement that is
1198                     // `let <pat> = <pat>;`. We re-use the original argument's pattern so that
1199                     // `HirId`s are densely assigned.
1200                     let expr = this.expr_ident(desugared_span, ident, new_parameter_id);
1201                     let stmt = this.stmt_let_pat(
1202                         stmt_attrs,
1203                         desugared_span,
1204                         Some(P(expr)),
1205                         parameter.pat,
1206                         hir::LocalSource::AsyncFn
1207                     );
1208                     statements.push(stmt);
1209                 } else {
1210                     // If this is not the simple case, then we construct two statements:
1211                     //
1212                     // ```
1213                     // let __argN = __argN;
1214                     // let <pat> = __argN;
1215                     // ```
1216                     //
1217                     // The first statement moves the parameter into the closure and thus ensures
1218                     // that the drop order is correct.
1219                     //
1220                     // The second statement creates the bindings that the user wrote.
1221
1222                     // Construct the `let mut __argN = __argN;` statement. It must be a mut binding
1223                     // because the user may have specified a `ref mut` binding in the next
1224                     // statement.
1225                     let (move_pat, move_id) = this.pat_ident_binding_mode(
1226                         desugared_span, ident, hir::BindingAnnotation::Mutable);
1227                     let move_expr = this.expr_ident(desugared_span, ident, new_parameter_id);
1228                     let move_stmt = this.stmt_let_pat(
1229                         ThinVec::new(),
1230                         desugared_span,
1231                         Some(P(move_expr)),
1232                         move_pat,
1233                         hir::LocalSource::AsyncFn
1234                     );
1235
1236                     // Construct the `let <pat> = __argN;` statement. We re-use the original
1237                     // parameter's pattern so that `HirId`s are densely assigned.
1238                     let pattern_expr = this.expr_ident(desugared_span, ident, move_id);
1239                     let pattern_stmt = this.stmt_let_pat(
1240                         stmt_attrs,
1241                         desugared_span,
1242                         Some(P(pattern_expr)),
1243                         parameter.pat,
1244                         hir::LocalSource::AsyncFn
1245                     );
1246
1247                     statements.push(move_stmt);
1248                     statements.push(pattern_stmt);
1249                 };
1250
1251                 parameters.push(new_parameter);
1252             }
1253
1254             let body_span = body.map_or(span, |b| b.span);
1255             let async_expr = this.make_async_expr(
1256                 CaptureBy::Value,
1257                 closure_id,
1258                 None,
1259                 body_span,
1260                 hir::AsyncGeneratorKind::Fn,
1261                 |this| {
1262                     // Create a block from the user's function body:
1263                     let user_body = this.lower_block_expr_opt(body_span, body);
1264
1265                     // Transform into `drop-temps { <user-body> }`, an expression:
1266                     let desugared_span = this.mark_span_with_reason(
1267                         DesugaringKind::Async,
1268                         user_body.span,
1269                         None,
1270                     );
1271                     let user_body = this.expr_drop_temps(
1272                         desugared_span,
1273                         P(user_body),
1274                         ThinVec::new(),
1275                     );
1276
1277                     // As noted above, create the final block like
1278                     //
1279                     // ```
1280                     // {
1281                     //   let $param_pattern = $raw_param;
1282                     //   ...
1283                     //   drop-temps { <user-body> }
1284                     // }
1285                     // ```
1286                     let body = this.block_all(
1287                         desugared_span,
1288                         statements.into(),
1289                         Some(P(user_body)),
1290                     );
1291                     this.expr_block(P(body), ThinVec::new())
1292                 });
1293             (HirVec::from(parameters), this.expr(body_span, async_expr, ThinVec::new()))
1294         })
1295     }
1296
1297     fn lower_method_sig(
1298         &mut self,
1299         generics: &Generics,
1300         sig: &FnSig,
1301         fn_def_id: DefId,
1302         impl_trait_return_allow: bool,
1303         is_async: Option<NodeId>,
1304     ) -> (hir::Generics, hir::FnSig) {
1305         let header = self.lower_fn_header(sig.header);
1306         let (generics, decl) = self.add_in_band_defs(
1307             generics,
1308             fn_def_id,
1309             AnonymousLifetimeMode::PassThrough,
1310             |this, idty| this.lower_fn_decl(
1311                 &sig.decl,
1312                 Some((fn_def_id, idty)),
1313                 impl_trait_return_allow,
1314                 is_async,
1315             ),
1316         );
1317         (generics, hir::FnSig { header, decl })
1318     }
1319
1320     fn lower_fn_header(&mut self, h: FnHeader) -> hir::FnHeader {
1321         hir::FnHeader {
1322             unsafety: h.unsafety,
1323             asyncness: self.lower_asyncness(h.asyncness.node),
1324             constness: h.constness.node,
1325             abi: self.lower_extern(h.ext),
1326         }
1327     }
1328
1329     pub(super) fn lower_abi(&mut self, abi: StrLit) -> abi::Abi {
1330         abi::lookup(&abi.symbol_unescaped.as_str()).unwrap_or_else(|| {
1331             self.error_on_invalid_abi(abi);
1332             abi::Abi::Rust
1333         })
1334     }
1335
1336     pub(super) fn lower_extern(&mut self, ext: Extern) -> abi::Abi {
1337         match ext {
1338             Extern::None => abi::Abi::Rust,
1339             Extern::Implicit => abi::Abi::C,
1340             Extern::Explicit(abi) => self.lower_abi(abi),
1341         }
1342     }
1343
1344     fn error_on_invalid_abi(&self, abi: StrLit) {
1345         struct_span_err!(
1346             self.sess,
1347             abi.span,
1348             E0703,
1349             "invalid ABI: found `{}`",
1350             abi.symbol
1351         )
1352         .span_label(abi.span, "invalid ABI")
1353         .help(&format!("valid ABIs: {}", abi::all_names().join(", ")))
1354         .emit();
1355     }
1356
1357     fn lower_asyncness(&mut self, a: IsAsync) -> hir::IsAsync {
1358         match a {
1359             IsAsync::Async { .. } => hir::IsAsync::Async,
1360             IsAsync::NotAsync => hir::IsAsync::NotAsync,
1361         }
1362     }
1363
1364     pub(super) fn lower_generics(
1365         &mut self,
1366         generics: &Generics,
1367         itctx: ImplTraitContext<'_>)
1368         -> hir::Generics
1369     {
1370         // Collect `?Trait` bounds in where clause and move them to parameter definitions.
1371         // FIXME: this could probably be done with less rightward drift. It also looks like two
1372         // control paths where `report_error` is called are the only paths that advance to after the
1373         // match statement, so the error reporting could probably just be moved there.
1374         let mut add_bounds: NodeMap<Vec<_>> = Default::default();
1375         for pred in &generics.where_clause.predicates {
1376             if let WherePredicate::BoundPredicate(ref bound_pred) = *pred {
1377                 'next_bound: for bound in &bound_pred.bounds {
1378                     if let GenericBound::Trait(_, TraitBoundModifier::Maybe) = *bound {
1379                         let report_error = |this: &mut Self| {
1380                             this.diagnostic().span_err(
1381                                 bound_pred.bounded_ty.span,
1382                                 "`?Trait` bounds are only permitted at the \
1383                                  point where a type parameter is declared",
1384                             );
1385                         };
1386                         // Check if the where clause type is a plain type parameter.
1387                         match bound_pred.bounded_ty.kind {
1388                             TyKind::Path(None, ref path)
1389                                 if path.segments.len() == 1
1390                                     && bound_pred.bound_generic_params.is_empty() =>
1391                             {
1392                                 if let Some(Res::Def(DefKind::TyParam, def_id)) = self.resolver
1393                                     .get_partial_res(bound_pred.bounded_ty.id)
1394                                     .map(|d| d.base_res())
1395                                 {
1396                                     if let Some(node_id) =
1397                                         self.resolver.definitions().as_local_node_id(def_id)
1398                                     {
1399                                         for param in &generics.params {
1400                                             match param.kind {
1401                                                 GenericParamKind::Type { .. } => {
1402                                                     if node_id == param.id {
1403                                                         add_bounds.entry(param.id)
1404                                                             .or_default()
1405                                                             .push(bound.clone());
1406                                                         continue 'next_bound;
1407                                                     }
1408                                                 }
1409                                                 _ => {}
1410                                             }
1411                                         }
1412                                     }
1413                                 }
1414                                 report_error(self)
1415                             }
1416                             _ => report_error(self),
1417                         }
1418                     }
1419                 }
1420             }
1421         }
1422
1423         hir::Generics {
1424             params: self.lower_generic_params(&generics.params, &add_bounds, itctx),
1425             where_clause: self.lower_where_clause(&generics.where_clause),
1426             span: generics.span,
1427         }
1428     }
1429
1430     fn lower_where_clause(&mut self, wc: &WhereClause) -> hir::WhereClause {
1431         self.with_anonymous_lifetime_mode(
1432             AnonymousLifetimeMode::ReportError,
1433             |this| {
1434                 hir::WhereClause {
1435                     predicates: wc.predicates
1436                         .iter()
1437                         .map(|predicate| this.lower_where_predicate(predicate))
1438                         .collect(),
1439                     span: wc.span,
1440                 }
1441             },
1442         )
1443     }
1444
1445     fn lower_where_predicate(&mut self, pred: &WherePredicate) -> hir::WherePredicate {
1446         match *pred {
1447             WherePredicate::BoundPredicate(WhereBoundPredicate {
1448                 ref bound_generic_params,
1449                 ref bounded_ty,
1450                 ref bounds,
1451                 span,
1452             }) => {
1453                 self.with_in_scope_lifetime_defs(
1454                     &bound_generic_params,
1455                     |this| {
1456                         hir::WherePredicate::BoundPredicate(hir::WhereBoundPredicate {
1457                             bound_generic_params: this.lower_generic_params(
1458                                 bound_generic_params,
1459                                 &NodeMap::default(),
1460                                 ImplTraitContext::disallowed(),
1461                             ),
1462                             bounded_ty: this.lower_ty(bounded_ty, ImplTraitContext::disallowed()),
1463                             bounds: bounds
1464                                 .iter()
1465                                 .filter_map(|bound| match *bound {
1466                                     // Ignore `?Trait` bounds.
1467                                     // They were copied into type parameters already.
1468                                     GenericBound::Trait(_, TraitBoundModifier::Maybe) => None,
1469                                     _ => Some(this.lower_param_bound(
1470                                         bound,
1471                                         ImplTraitContext::disallowed(),
1472                                     )),
1473                                 })
1474                                 .collect(),
1475                             span,
1476                         })
1477                     },
1478                 )
1479             }
1480             WherePredicate::RegionPredicate(WhereRegionPredicate {
1481                 ref lifetime,
1482                 ref bounds,
1483                 span,
1484             }) => hir::WherePredicate::RegionPredicate(hir::WhereRegionPredicate {
1485                 span,
1486                 lifetime: self.lower_lifetime(lifetime),
1487                 bounds: self.lower_param_bounds(bounds, ImplTraitContext::disallowed()),
1488             }),
1489             WherePredicate::EqPredicate(WhereEqPredicate {
1490                 id,
1491                 ref lhs_ty,
1492                 ref rhs_ty,
1493                 span,
1494             }) => {
1495                 hir::WherePredicate::EqPredicate(hir::WhereEqPredicate {
1496                     hir_id: self.lower_node_id(id),
1497                     lhs_ty: self.lower_ty(lhs_ty, ImplTraitContext::disallowed()),
1498                     rhs_ty: self.lower_ty(rhs_ty, ImplTraitContext::disallowed()),
1499                     span,
1500                 })
1501             },
1502         }
1503     }
1504 }